1. Field of the Invention
The present invention relates to a running control device for an industrial vehicle such as a forklift or the like.
2. Description of the Related Art
In order to improve driving operability and perform work with good efficiency, vehicles equipped with a torque converter and a transmission having clutches used for switching between forward and reverse and for speed stage changes are widely used as industrial vehicles such as forklifts and the like. In the case of such industrial vehicles, an operation in which the forward-reverse lever is switched from the current traveling direction of the vehicle to the opposite direction is frequently performed during the running of the vehicle; in this case, it is necessary to ensure that the vehicle can run smoothly without any shock during forward-reverse changeover.
For example, a technique which is devised so that when the forward-reverse operating lever is switched over, operating oil is supplied to the braking device so that the vehicle is decelerated until the vehicle is reversed to the traveling direction selected by the forward-reverse operating lever, and the brakes are then let off after the traveling direction has been reversed, has been proposed as one conventional control method technique for solving this problem (e.g., see Japanese Patent Application Laid-Open No. 2002-79926 (pages 5–6, FIGS. 3–4). According to this patent application, when, for example, the forward-reverse operating lever is switched from the “forward position” to the “reverse position”, braking is applied by the braking force of the brake corresponding to the vehicle speed so that the vehicle is caused to decelerate; then, when the traveling direction is switched to the reverse direction after the vehicle stops, and the vehicle begins to travel in the reverse direction, the “forward travel” signal in the brake control circuit is switched “off”, so that a specified relay is switched “off”. As a result, the control oil is cut off, so that the brake is released.
However, when the abovementioned conventional technique disclosed in Japanese Patent Application Laid-Open No. 2002-79926 is used, although the braking force is actuated in accordance with the vehicle speed, this braking force is actuated until the vehicle speed reaches zero, and when the brake is subsequently let off, there is an operating delay time until the brake is completely released; accordingly, with the vehicle speed of zero as a boundary, the braking torque acts in the opposite direction from the vehicle acceleration torque. In other words, for a speed change without any shock, it is necessary that the fluctuation in the acceleration and deceleration of the vehicle itself during the speed change be small; however, in the abovementioned technique, since the braking torque constantly acts as a braking torque, the acceleration of the vehicle itself is caused to fluctuate greatly by the effect of this braking torque when the traveling direction of the vehicle is reversed. Consequently, the following problem arises: namely, a speed change shock is generated in the vicinity of a vehicle speed of zero, so that a smooth speed change operation cannot be accomplished. Furthermore, since the driving force of the hydraulic clutch is forcibly suppressed by the brake after the traveling direction is reversed, the following problem arises: namely, not only is there an energy loss, but also a drop in the durability of the brake and hydraulic clutch.